Impact of Vessel Noise at Wattle Grove · The Ronja Huon is a new vessel that is currently under...

Department of Primary Industries, Parks, Water and Environment

NOISE REPORT – NLR 2015-02

Impact of Vessel Noise

at Wattle Grove

July 2015

Impact of Vessel Noise at Wattle Grove

NLR 2015-02 Page 2 of 27

DOCUMENT CONTROL

Title: Impact of Vessel Noise at Wattle Grove Report Number: NLR 2015-02 Prepared by: Scientific and Technical Branch EPA Division Department of Primary Industries, Parks, Water and Environment GPO Box 1751, Hobart, Tas. 7000. Contact: Bill Wilson Telephone: 03 6165 4583 FAX: 03 6233 3800 Email: [email protected] Copyright: State of Tasmania 2015 Keywords: Vessel, Boat, Noise, Marine Farming Data sets: S-332, S-333, S-334, S-335, Confidentiality Status: Public – no cause for restriction

Author: Bill Wilson Date: 31 July 2015

Reviewed by: Mark Stanborough Date: 31 July 2015

Revision History

Revision Number Date of Issue Details

0 31/07/2015 Version 1

1 (07/07/2015) - typos Version 1.1

mailto:[email protected]


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Summary

This report investigates the noise emitted by a vessel used for servicing marine farms. The

vessel, Ronja Huon, is a relatively new vessel and its operations in the Huon River and

D’entrecasteaux Channel has resulted in a number of complaints regarding the noise

emitted by the vessel.

Aspects of the noise from the vessel have been identified and it can be concluded that the

main component of the noise is a significant tonal peak at 45 Hz. The energy in this peak

dominates the noise and is almost totally responsible for the resulting A-weighted noise

level at any distance from the vessel.

The noise from the vessel also contains many smaller tonal peaks that are within a series of

harmonics based on a fundamental of 7.5 Hz.

The results are consistent with the vessel complying with the 74 dB(A) at 25 metre limit in

Regulation 8(1) of the Environmental and Pollution Control (Miscellaneous Noise) Regulations

2014.

Introduction

The Ronja Huon is a new vessel that is currently under contract to Huon Aquaculture to

provide support for marine farming activities in the lower Huon River, Channel and eastern

side of Bruny Island.

The vessel started operation at the beginning of 2015. Unfortunately, it was setup for 60Hz

shore-power which is generally not available in Australia. Consequently it was necessary to

keep the on-board generators running when the vessel was in port for both routine

restocking and extended maintenance and operational adjustments. This situation has been

rectified and shore-power for the vessel is now available at Port Huon.

Complaints have been received by several agencies regarding noise from the vessel. These

complaints relate to the operation of ship’s generators in Port Huon, the transit of the

vessel in front of residences on the riverbanks of the Huon River or the operation of the

vessel at leases near the mouth of the Huon River as heard from areas such as Roaring

Beach (Surveyors Bay) and Lunawanna (Bruny Island).

These complaints represent a considerable range of source to receiver distances, from

some hundreds of metres for Port Huon residents hearing the vessel at the Port Huon pier

to well over 10 km for on-lease noise reaching Lunawanna.

This report provides details and interpretation of acoustic measurements made of the vessel

noise in the Huon River and D’entrecasteaux Channel areas.


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Vessel Details

The Ronja Huon is described as a Well Boat. It has three 1000 tonne water holds and has a

gross weight of 3566 tonnes. Its home port is Aalesund, Norway, and it sails under the

Norwegian flag.

The vessel is owned by Sølvtrans, with web address Sølvtrans.NO, who has a fleet of these

wellboats which are mainly employed on log-term contracts in Norway, Scotland, Canada,

Chile and Australia.

The vessel is 76 metres long and the height of the engine exhaust stack above the water

level has been estimated to be about 15 metres. The main propulsion utilises power from a

pair of 2MW diesel-electric generators, which are believed to provide electricity for all

other services.

The main noise sources on the vessel are expected to include the main engine exhausts,

engine and pump noise radiated through the hull, and noise from deck-based equipment.

Vessel Movements

It has been possible to follow the general movements of the vessel using data provided by

AIS (Automatic Identification System) via web-based providers. The intention has been to

use this data to indicate typical courses, locations and speeds in relation to measurement

locations.

Some measurements had been made before AIS locations were collected. This relates to

noise measurements at Wattle Grove and Port Huon. Some vessel positions can be

inferred from variations in the measured noise levels, such as the time of closest approach

to the Wattle Grove site and times of arrival and departure at Port Huon.

At Port Huon it appears that the vessel is located on the western side of the pier at

Lat -43.159540, Lon 146.975600 or 498016mE, 5221468mN.

Measurement Locations

This investigation into noise from Ronja Huon is based on measurements and audio

recordings made at five main locations. The choice of these locations has been based, in

part, on direct complaints regarding disturbance from vessel noise. The locations are not

intended to provide a definitive evaluation of the noise leading to complaints but rather

provide useful measurements of vessel noise from different distances and different

directions. At the same time, the ambient noise conditions will vary significantly. All sites

are close to the coastline and thus will be influenced by noise from wave action.


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Site Latitude Longitude Easting Northing

Port Huon -43.165903 146.973021 497807mE 5221760mN

Wattle Grove -43.177975 146.987671 498998mE 5219421mN

Nebraska Beach -43.071338 147.349393 528445mE 5231203mN

Roaring Beach -43.289859 147.091789 507447mE 5206992mN

Lunawanna -43.349140 147.225343 518263mE 5200288mN

Survey details are included in Appendix A.

Equipment

Measurements were made with Acoustic Research Laboratories Ngara noise loggers. These

units measure both A and C frequency weighted noise levels at a rate of 10 measurements per second. The loggers also capture a high quality audio recording in one-hour segments.

Typically the memory capacity will provide for about 8 days of operation.

Many environmental noise limits are specified as A-weighted values. This particular

frequency weighting is intended to adjust the measurements to align to the frequency

response of the human ear. However, it appears to underestimate the response to low-

frequency sounds.

C-weighting is an alternative frequency weighting which includes significantly more low-

frequency sound that A-weighting and has been used to advantage to identify noise from the

Ronja Huon.

The loggers were calibrated with a Bruel and Kjaer Type 4231 field calibrator before and

after deployment.

Results from Port Huon and Wattle Grove

Noise loggers were deployed at both Port Huon and Wattle Grove from 05 to 11 February

2015 and then followed by a second deployment from 12 to 20 February 2015. Graphical

noise level results for the deployments are provided in Appendix B.

During the two deployments the Ronja Huon docked at Port Huon once arriving at about

5:30 pm on 10 February and departing at about 10:00 pm the same day.

Although it is conventional to use A-weighting results, much better clarity of noise from the

vessel is provided using C-weighted levels. In addition, noise loggers record at a rate of 10 measurements per second which are then grouped into more convenient time segments,

typically 5-minutes. This provides a statistical distribution of the noise during each 5-minute


NLR 2015-02 Page 6 of 27

period. This scheme has the advantage that particular components of the noise can be

separated out for investigation. The vessel noise is fairly constant and will thus control the

lower part of the statistical distribution of the noise. Short, high-level sources of noise, such

as passing cars and bird calls, can be very significant contributors to the average noise level

and will tend to mask the constant, lower-level contributors. It is possible to exclude the

short-term elevated noise by choosing a statistic, such as the L90, which is the noise level

exceeded for 90% of the time.

Figure 1 shows the variation of the L90, C-weighted sound pressure level for a 12 hour

period starting at midday on 10/02/2015. The noise level at the Port Huon monitoring site

increases as the vessel arrives, between 5:00 and 6:00 pm, and there is a similar increase

when the vessel leaves at 10:00 pm. Between these times the noise level is fairly constant at

60 dB(C), indicating that the boat noise is dominant during the intervening period.

Figure 1. Time plot of the L90, C-weighted sound pressure level at S-332 (Wattle

Grove, blue) and S-333 (Port Huon, magenta)

The delineation of the noise from the vessel is quite obvious at the Port Huon monitoring

site, due to the increase in noise level at arrival and departure and due to the constant noise

level whilst the vessel is at the dock.

The increase in noise as the vessel passes the Wattle Grove site can be identified in relation

to the variation in noise level at Port Huon. The increase during arrival is not as obvious as

during departure, primarily due to the level of the background noise. It can be seen from

figure 1 that the noise level at the Wattle Grove site was about 40 dB(C) before the

approach of the Ronja Huon and had reduced to about 30 dB(C) after departure.


NLR 2015-02 Page 7 of 27

The vessel noise measured at Wattle Grove produced a level of about 60 dB(C) on arrival

and 63 dB(C) on departure. The departure peak is more obvious due to the reduced

background noise.

The A-weighted sound pressure levels recorded at the two sites are presented in Figure 2

for the corresponding time period as figure 1. The clarity provided by figure 1 is not

present in figure 2 but it is possible to extract some useful information by relying on the

timing provided in figure 1.

Figure 2. Time plot of the L90, A-weighted sound pressure level at S-332 (Wattle

Grove, blue) and S-333 (Port Huon, magenta) for the same period as figure 1

The noise level at Port Huon appears to be fairly constant at about 40 dB(A) whilst the

vessel was in port, apart from a 30 minute period at about 8:30pm when there is a significant increase at both measurement sites, followed by a reduction of several dB(A) at

Port Huon towards the end of the time in port. There was a reduction of about 6 dB(A) in

the noise level at the Port Huon site when the vessel departed.

At the Wattle Grove site the noise level was about 27 dB(A) before the vessel departed and

reached a maximum of about 40 dB(A) as the vessel passed, then dropped to about 24

dB(A). It can be seen from figures 1 and 2 that the best signal to noise ratio to measure the

properties of the sound from the Ronja Huon is during its pass-by of the Wattle Grove site.


NLR 2015-02 Page 8 of 27

The exact path of the vessel as it passed Wattle Grove on 10 February 2015 is not known

but trajectories derived from AIS data indicate that the vessel tended to follow a similar

path past Wattle Grove, which would be expected for a vessel of this size. The distance

from the measurement site to the point of closest approach, as shown in Figure 3, is about

825 metres. Errors propagated to noise level determinations resulting from an error in the

separation distance will, however, be minimal.

The attenuation of sound intensity with distance is generally dominated by divergence but

for distances over about 500 metres the influence of air absorption becomes important. Air

absorption is frequency dependent with attenuation increasing with frequency. It is

necessary to take air absorption into account as the frequency spectrum measured at 825

metres will have been modified from the emitted spectrum. Since the emission spectrum is

not known, it can be determined from the received spectrum and the theoretical air

absorption.

Figure 3. Closest approach to the Wattle Grove measuring site, based on

several vessel trajectories. The yellow line is 825 metres long.

One-third octave spectra of the noise at the Wattle Grove site have been determined for a

series of short time periods, between 1 and 2 minutes each, whilst the vessel was moving

past. The timing of the spectra relative to the passage of the vessel is shown in Figure 4.

Spectrum 4 was centred on the time of peak noise and has corresponding broad-band levels

of 70 dB(lin), 67 dB(C) and 43 dB(A). One additional spectrum, spectrum 9, was measured

about 50 minutes after the time of closest approach. The levels derived from spectrum 4


NLR 2015-02 Page 9 of 27

are expected to be slightly lower than the peak levels indicated in figure 4 because the

spectrum has been averaged over a greater period that the levels indicated in the figure.

Only spectra 3, 4 and 9 will be considered at this stage. There is a peak immediately before

the time period for spectrum 3. This peak, which is more obvious in the A-weighted trace

than the C-weighted trace, is due to a passing car.

One-third octave spectra 3, 4 and 9 are shown in Figure 5 and the same spectra, but A-

weighted, are shown in Figure 6. In general, spectrum 9 can be regarded as indicating the

ambient background conditions, i.e. the general acoustic conditions in the absence of the

vessel.

Figure 4. Sound pressure level at the Wattle Grove measuring site, both A and

C weighted. Frequency spectra have been measured at the eight indicated

periods and 50 minutes after the time of the peak noise level.

1 2 3 4 5 6 7 8


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Figure 5. One-third octave spectra 3, 4, and 9

Figure 6. A-weighted one-third octave spectra 3, 4 and 9


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The main peak in the 50 Hz band is very apparent for spectra 3 and 4, extending about 20

dB(A) above the neighbouring bands. In addition, the 100 Hz and 200 Hz bands are

elevated, which would be consistent with harmonics of the energy in the 50 Hz band. There

is a broad peak from about 400 Hz to 2 kHz but this is not identical for spectra 3 and 4.

In general, the background one-third octave levels indicated by spectrum 9 are more than

15 to 30 dB below the levels when the vessel is at closest approach. However, the 2 kHz to

4 kHz bands are significantly elevated in all spectra and it is highly likely that this relates to

noise from nearby insects. Clearly this band of energy is not due to the vessel and has to be

removed from the levels in spectrum 4 to determine the contribution from the vessel.

There is a hint of the main tonal peak of the vessel noise in the 50 Hz one-third octave band

but no other evidence of a contribution of vessel noise in spectrum 9.

The method for removing the insect noise peak from spectrum 4 could have some influence

on the final sound power determination, particularly for an A-weighted value. However, the

main interest will ultimately be on long-range propagation and so this part of the emission

spectrum will be of minimal importance. The 1.6 kHz band (23.6 dB) is clearly dominated

by vessel noise but the next band at 2.0 kHz (22.9 dB) is clearly dominated by insect noise. It is considered that a reduction of the levels in the bands from 2.0 to 5.0 kHz down to 10

dB would give an acceptable approximation for the vessel spectrum. The resultant change is

0.4 dB(A) which indicates that the insect noise has minimal influence on the A-weighted

noise level. It is likely that the energy at higher frequency bands (5 kHz and above) is also

unrelated to the vessel.

Some additional clarification can be extracted from similar data measured at the Port Huon

measurement site. At 10 pm when the vessel departed the port, the noise level dropped

from about 66 dB(C) by about 20 dB to about 46 dB(C). This does not provide as much

signal to noise ratio as provided in the Wattle Grove measurements but the reduced

separation provides a little less high-frequency attenuation. One-third octave spectra with

both the vessel present and absent are shown in Figure 7. As expected, the otherwise

ambient noise was greater at the Port Huon site. There is no indication of insect noise and

there is an indication of an increase in sound level due to the vessel up to about 4kHz.


NLR 2015-02 Page 12 of 27

Figure 7. One-third octave spectra with and without the vessel as measured at

the Port Huon site

High-resolution spectra, corresponding to spectra 3, 4 and 9 discussed earlier, are provided

in Figure 8. These spectra show that the vessel noise includes many tonal peaks with a

dominant peak at 45 Hz. Other strong peaks are harmonics of the 45 Hz at 90 Hz and 180

Hz. There are many other tonal peaks that align to a regular spacing of 7.5 Hz that extend

from 22.5 Hz up to about 300 Hz and possibly higher.

The main 45 Hz peak for spectrum 4 has a level of 69 dB and has sufficient energy to

completely dominate the corresponding 50Hz one-third octave band level.


NLR 2015-02 Page 13 of 27

Figure 8. High-resolution spectra corresponding to the one-third octave spectra

shown in figure 6 The vertical gridlines are spaced every 7.5 Hz.

To provide some additional clarity regarding the propagation and direction of emission, a

vessel position mid-way between the Port Huon and Wattle Grove measurement sites has

been identified, as shown in Figure 9. This position is 1350 metres from the two

measurement sites and 1040 metres from the point of closest approach to Wattle Grove.

From other measurements it is believed that the vessel was travelling at about 4.3 metres

per second and, at this speed, would have taken 242 seconds (4 min 2 sec) to move from

the mid-point to the position of closest approach to Wattle Grove. Figure 10 is a plot of

the level of the 45 Hz peak as the vessel moves down the Huon River. The time axis is

relative to the peak at Wattle Grove which is assumed to indicate the time of closest

approach to the Wattle Grove measurement site. At 242 seconds before the time of

closest approach the respective noise levels at Port Huon and Wattle Grove were 66 and

57 dB. This difference of 9 dB is not expected, nor is the behaviour of the levels as the

vessel continues down river. In particular, it is expected that after the closest approach to Wattle Grove, the level at Port Huon will always be lower than the level at Wattle Grove –

which is clearly not the case.

There are several possible causes of these unexpected observations, including directional

noise from the vessel, meteorological influences and topographic screening. There are also

some other indications of unexplained influences for long distance propagation.

-10

0

10

20

30

40

50

60

70

80

0 45 90 135 180 225 270 315 360 405 450 495

Sou

nd

pre

ssu

re le

vel (

dB

/Hz)

Frequency (Hz)

High-resolution spectra for pass-by at Wattle Grove

spec-3

spec-4

spec-9


NLR 2015-02 Page 14 of 27

Figure 9. The position labelled ‘mid-point’ is equidistant for the Port Huon and

Wattle Grove measurement sites

Figure 10. Level of the 45 Hz peak as measured from Port Huon (PH, blue) and

Wattle Grove (WG, red) The vessel was mid-way between the monitoring sites

at -242 seconds.

20

25

30

35

40

45

50

55

60

65

70

75

80

-500 -400 -300 -200 -100 0 100 200 300 400 500

Leve

l of

44

to

46

Hz

(dB

)

Time relative to closest approach to Wattle Grove (sec)

Levels recorded at Port Huon and Wattle Grove during vessel departure

PH

WG


NLR 2015-02 Page 15 of 27

It has not been possible to resolve all the differences between the Port Huon, Wattle Grove

and the mid-point results but it is clear that the vessel noise is dominated by the main tonal

peak at 45 Hz that reports to the 50 Hz one-third octave band. At the time of closest

approach to Wattle Grove this peak represents an unweighted noise level of 69 dB. The

corresponding C and A-weighted levels are 70 dB(C) and 42 dB(A) respectively.

Variation in the Frequency Spectrum

There is a variation in the fine detail of the frequency spectrum in the vicinity of the main 45

Hz tonal peak. The variation with time of the spectral shape has been reviewed by spectral

analysis at 1 Hz resolution, although it appears that the variations occur well below this

resolution. The variation for the 44 to 48 Hz bands are shown in Figure 11 and it can be

seen that 45 and 46 Hz are the maximum components before the 530 second peak but that

44 and 45 Hz are the maximum components after the 530 second peak.

Figure 11. Fine frequency profiles as the vessel passes Wattle Grove

This indicates a variation in the frequency of the main energy peak consistent with Doppler

shift, i.e. the pitch is slightly elevated as the vessel approaches the recorder and then drops

as the vessel passes and travels away. This variation in frequency has been estimated from

the amplitude of the 44, 45 and 46 Hz levels and the result of this frequency determination

has been plotted in Figure 12. It can be seen from the figure that there is an initial rise in

frequency to about 45.6 Hz followed by a fall through a point of inflection at about 530

-80

-75

-70

-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

0 200 400 600 800 1000 1200 1400 1600 1800

Sou

nd

pre

ssu

re (

dB

re

lati

ve)

Time - seconds after 2200H, 10/02/2014 (Summer Time)

Fine frequency profile - passing Wattle Grove

44Hz

45Hz

46Hz

47Hz

48Hz


NLR 2015-02 Page 16 of 27

seconds to a minimum at about 700 seconds. There is a then a rise to about 45.0 Hz at

about 820 seconds followed by a drop to about 44.5 Hz.

The interpretation is an initial rise in frequency due to the vessel accelerating from rest at

the Port Huon pier, reaching a steady speed at about 200 seconds on the Figure 12 time

axis, and then there is a classic Doppler profile as the vessel moves past the recording site.

The local peak at about 820 seconds on Figure 12 is due to the bend in the vessel’s path

around Bullock and Brabazon Points.

The approach frequency is 45.60 Hz and the depart frequency is 44.45 Hz. Assuming the

speed of sound is 340 m/s, the variation in frequency is consistent with a Doppler variation

from a source travelling at 4.3 m/s (8.4 knots).

Figure 12. Variation in frequency of the main ~45 Hz spectral peak measured at

Wattle Grove as the vessel departs from Port Huon.

Other Measurement Sites

In addition to the Wattle Grove site, several other measurement sites have been utilised to

provide a range of vessel to receiver distances. Descriptions of the other sites are provided

below together with measured spectra of vessel noise. There are 15 spectra taken at a

range of distances from the vessel.

43.5

44

44.5

45

45.5

46

46.5

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Mai

n f

req

ue

ncy

pe

ak (

Hz)

Time - seconds after 2200H, 10/02/2014 (Summer Time)

Frequency of main peak (near 45 Hz) - passing Wattle Grove


NLR 2015-02 Page 17 of 27

Nebraska Beach

The vessel passed the Nebraska Beach measurement site during the period 1pm to 3pm on

31/03/2015. There is a lease on the outside of Bruny Island and the vessel accesses this

lease about once a week. This measurement site, towards the southern end of Nebraska

Beach, was chosen due to the relatively simple waterway and the access to a suitable

measurement site. There have not been any representations regarding the vessel from

residents in the upper sections of the D’entrecasteaux Channel. The course of the vessel

between Tinderbox and the Nebraska site is fairly constrained and it is expected that the

vessel will always pass at a similar distance from the shore. The distance to closest

approach has been estimated at about 1150 m.

Figure 13. Vessel spectrum at Nebraska Beach

Roaring Beach

The vessel spends a significant proportion of time at the mouth of the Huon River servicing

leases between Roaring Beach and Huon Island and SSE of Roaring Beach. The site was

chosen as a result of complaints.

0

10

20

30

40

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60

70

0 45 90 135 180 225 270 315 360 405 450 495

Sou

nd

pre

ssu

re le

vel (

dB

)

Frequency (Hz)

Spectra of Pass-By Measurements - Nebraska Beach

set 11


NLR 2015-02 Page 18 of 27

Figure 14. Vessel spectra measured at Roaring Beach

Lunawanna

To the south-east of the Roaring Beach leases are several lease areas at Zuidpool. The

Lunawanna site was chosen as a result of complaints. At the time of the first complaint, the

vessel was tracked by AIS to be about 11 km WNW of Lunawanna and it was considered

surprising that the vessel could be heard consistently at such a distance.

0

10

20

30

40

50

60

70

0 45 90 135 180 225 270 315 360 405 450 495

Sou

nd

pre

ssu

re le

vel (

dB

)

Frequency (Hz)

Spectra of Measurements at Roaring Beach

set 4

set 5

set 6

set 7

set 9


NLR 2015-02 Page 19 of 27

Figure 15. Vessel spectra measured at Lunawanna

Petcheys Bay

Various complaints regarding noise have been received from the Petcheys Bay area

regarding various aspects of marine farming. Currently the nearby leases are not actively

used but boat noise is still leading to complaints. A recent monitoring exercise has provided

an opportunity to measure the Ronja Huon as the vessel passes on its way from Port Huon

to lease areas at the mouth of the Huon River. The vessel’s position was near Petcheys Bay

at 7am on 10/06/2015. Characteristic tonal harmonic pattern typical of the vessel was

detected between 0640H and 0655H on 10/06/2015.

-10

0

10

20

30

40

50

60

0 45 90 135 180 225 270 315 360 405 450 495

Sou

nd

pre

ssu

re le

vel (

dB

)

Frequency (Hz)

Spectra of Measurements at Lunawanna

set 1

set 2

set 3

set 8

set 10


NLR 2015-02 Page 20 of 27

Figure 16. Vessel spectra measured at Petcheys Bay

Deep Bay

AIS records indicate that the vessel was travelling to the SE as it passed Petcheys Bay on

10/06/2015. However, no acoustic signals were detected at Deep Bay consistent with the

Ronja Huon in the hours after the Petcheys Bay detection. It is interesting that noise from

the vessel was not detected, given that the vessel would have been in a direct line of sight at

about 6 km distance under fairly sheltered conditions.

Wattle Grove

There are two measured spectra provided for Wattle Grove, the first corresponds to the

vessel heading into Port Huon and the second is for the vessel after departing the port.

0

10

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50

60

0 45 90 135 180 225 270 315 360 405 450 495

Sou

nd

pre

ssu

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vel (

dB

)

Frequency (Hz)

Spectra of Pass-By Measurements - Petcheys Bay

set 12

set 13


NLR 2015-02 Page 21 of 27

Figure 17. Vessel spectra measured at Wattle Grove

Discussion

The previous results show that aspects of the noise from the Ronja Huon can be detected

at distances of many kilometres. This is most consistently achieved from the detection of

the tonal peak at 45 Hz but there are also contributions from the extensive harmonic series

of tones based on 7.5 Hz. Several significant variations in the harmonic series are noted,

such as the Petcheys Bay results that have every second harmonic completely missing,

whereas most other spectra include some peaks at 7.5 Hz separation.

The 45 Hz peak can be used as the prime measure of vessel noise. Most of the acoustic

energy is in the peak and, even though it is at a pitch that is attenuated significantly by the

human ear, it dominates the A-weighted level. Minor adjustments can be included,

depending on distance.

The level of the 45 Hz peak for each spectrum has been plotted against the estimated

distance to the vessel on Figure 18 below. The green triangle on the figure indicates the

level measured by Pitt and Sherry corresponding to 67 dB(A) at a reference distance of 25

metres. This indicates that the vessel complies with the 74 dB(A) limit specified in

Regulation 8(1) of the Environmental and Pollution Control (Miscellaneous Noise) Regulations

2014 and that the noise from the vessel reaching Wattle Grove is not unreasonable with

respect to the Regulation requirements.

0

10

20

30

40

50

60

70

0 45 90 135 180 225 270 315 360 405 450 495

Sou

nd

pre

ssu

re le

vel (

dB

)

Frequency (Hz)

Spectra of Pass-By Measurements - Wattle Grove

set 14

set 15


NLR 2015-02 Page 22 of 27

Figure 18 – Summary of results for the 45 Hz peak as a function of distance from

the vessel. The straight line is the classic drop of 6 dB per doubling in distance

and the green triangle point relates to a reference measurement at 25 metres.

(L=Lunawanna, RB=Roaring Beach, NB=Nebraska Beach, PB=Port Huon and

WG=Wattle Grove)

The results presented in figure 18 suggest there is a consistent elevation of vessel noise at

Lunawanna but that the results at the other sites are reasonably consistent with the straight

line representing a sound power of 125 dB and a drop of 6 dB per doubling in distance.

Since the noise from the vessel is dominated by a single tone, the propagation will be

influenced significantly by reflection of sound at the sea-surface. A discussion of this effect

has been included in Appendix C.

20

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40

50

60

70

80

90

100

10 100 1000 10000

Sou

nd

pre

ssu

re o

f m

ain

45

Hz

pe

ak (

dB

)

Distance from vessel (m)

Level of main tonal peak versus distance to vessel

P&S SWL=125 L RB NB PB WG


NLR 2015-02 Page 23 of 27

Appendix A – Measurement survey details

Data Set Location Comment Start Finish

S-332 Port Huon 1400h 05/02/2015 0900h 11/02/2015

S-333 Wattle Grove With S-332 1400h 05/02/2015 1000h 11/02/2015

S-334 Port Huon 1500h 12/02/2015 0800h 20/02/2015

S-335 Wattle Grove With S-334 1500h 12/02/2015 0800h 20/02/2015

S-339 Dennes Point 1300h 31/03/2015 0600h 08/04/2015

S-340 Lunawanna Only 4 hr 1200h 13/04/2015 1500h 08/04/2015

S-341 Roaring Beach 1600h 01/05/2015 1200h 08/05/2015

S-342 Lunawanna 1200h 04/05/2015 1200h 11/05/2015

S-343 Roaring Beach 1200h 08/05/2015 0400h 16/05/2015

S-344 Lunawanna 1200h 11/05/2015 0400h 19/05/2015

S-347 Petcheys Bay 1100h 05/06/2015 0300h 13/06/2015

S-348 Deep Bay 1200h 05/06/2015 0400h 13/06/2015


NLR 2015-02 Page 24 of 27

Appendix B – Plots of complete data sets for Wattle Grave and Port

Huon

Figure B1 – Noise levels for 05 – 12 February 2015 at Wattle Grove

Figure B2 – Noise levels for 12 – 20 January 2015 at Wattle Grove


NLR 2015-02 Page 25 of 27

Figure B3 – Noise levels for 05 to 12 February 2015 at Port Huon

Figure B4 – Noise levels for 12 to 21 February 2015 at Port Huon


NLR 2015-02 Page 26 of 27

Appendix C – Enhancement from sea surface reflection

Sound emitted from the vessel may reach a measurement site by several paths. Of

particular interest here is the interaction between the sound that propagates along the

direct line of sight and sound that reflects off the water surface. The two pathways will

result in two signals arriving at the receiver but with a slight time delay between the signals.

Because the sound from the vessel is dominated by a single tone, the addition of the two

signals has some very specific properties. If the time delay between the signals is negligible,

then the two signals will exhibit coherent addition which results in an increase in sound level

of 6 dB. Two random signals of equal amplitude will combine incoherently to produce a

resultant sound that is normally 3 dB greater that one of the signals. The increase of 6 dB

only occurs when the direct and the reflected signals are in phase and this tends to be the

case at low frequencies or for long propagation distances. It can also occur when the

difference between the direct and reflected signal paths is an integral number of

wavelengths. When the difference in the path lengths places the signals completely out of

phase, the two signals will cancel.

The graph below shows the expected enhancement due to reflection at the sea surface of

the sound from the vessel observed at Wattle Grove when the vessel is 825 metres away at

its point of closest approach. It can be seen that the 45 Hz emission will have virtually the

full 6 dB enhancement but harmonics near 170 Hz could be completely lost.

Figure C1 – Enhancement at Wattle Grove due to reflection by the sea surface

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Enhancement due to reflection at the sea surface


NLR 2015-02 Page 27 of 27

The figure shows that there is a comb filter produced by the interference where the

reductions are equally spaced along the frequency axis.

The same effect produces a change in signal strength as the distance between the source

and the receiving position change. The figure below shows the expected variation for a 45

Hz source 15 metres above the water surface and a receiver 28 metres above the water

surface, corresponding to the geometry of the Ronja Huon and Wattle Grove.

Figure C2 – Enhancement at 45 Hz as a function of source – receiver separation (for a

given lateral separation, the difference in direct and reflected path is shown in blue and the

corresponding enhancement is shown in red)

Note that for a frequency of 45 Hz there is no destructive interference for separation

distances beyond about 300 metres. All measurements in this investigation were made at

distances of 400 metres or greater from the vessel and so there will generally be a ground

enhancement of 6 dB inherent in all measurements at 45 Hz. Both enhancement and

destructive interference can be expected at frequencies above about 100Hz.

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Source to receiver separation distance (m)

Direct and ground-reflected path difference and consequent ehhancement

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